#! /bin/bash
###
### SSH wrapper to spawn separate SSH master connections on demand
###
### (c) 2010 Mark Wooding
###

###----- Licensing notice ---------------------------------------------------
###
### This program is free software; you can redistribute it and/or modify
### it under the terms of the GNU General Public License as published by
### the Free Software Foundation; either version 2 of the License, or
### (at your option) any later version.
###
### This program is distributed in the hope that it will be useful,
### but WITHOUT ANY WARRANTY; without even the implied warranty of
### MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
### GNU General Public License for more details.
###
### You should have received a copy of the GNU General Public License
### along with this program; if not, write to the Free Software Foundation,
### Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

###--------------------------------------------------------------------------
### Configuration.

: ${REAL_SSH=/usr/bin/ssh}
: ${SSH_HOME=$(unset HOME; bash -c 'echo ~/.ssh')}
: ${SSH_LOGDIR=$SSH_HOME/log-$(hostname)}

###--------------------------------------------------------------------------
### Parse the command line and dredge out information.

## This is a reasonable approximation to SSH's command-line argument parser.
unset host login
mode=m
declare -a opts masteropts
while :; do
  case "$1,$#" in

    ## Nothing left.  We're done.
    ,0)
      break
      ;;

    ## A command line option group.  Parse it and work out what's going on.
    -*)
      opt=$1
      opts=("${opts[@]}" "$opt")
      while :; do

	## Strip off the first character, because it's the one we dealt with
	## last time.
	opt=${opt#?}
	o=$opt

	## Phase 1: identify the option and whether it needs an argument.
	unset arg
	case "$o" in

	  ## Empty group.  We're done.
	  "")
	    break
	    ;;

	  ## Options with arguments.
	  [bcDeFiLlmOopRSw]*)
	    case "$#,$o" in

	      ## You're going to lose because there's no argument.  But we'll
	      ## let SSH deal with that.
	      1,?)
		arg=
		;;

	      ## There's an argument cuddled on to the end of the option.  It
	      ## will have been committed to the `opts' array as part of the
	      ## option group.
	      *,??*)
		arg=${opt#?}
		opt=
		;;

	      ## Nope.  There's an argument in the next word.  Grab it and
	      ## commit it.
	      *)
		arg="$2"
		opts=("${opts[@]}" "$arg")
		shift
		;;
	    esac
	    ;;

	  ## Anything else.  Let it go even if it's not valid: SSH will moan
	  ## if it wants.  Note that `--' is ignored by SSH, but this isn't
	  ## documented; in particular, `--' is /not/ a POSIX end-of-options
	  ## marker, so we don't try to handle it specially here either.
	  *)
	    ;;
	esac

	## Phase two.  Figure out whether what this means for us.
	case "$mode,$o" in

	  ## `-O foo' and `-S foo' mean that the caller wants to take
	  ## control of the multiplexing process.
	  ?,[MOS]*)
	    mode=p
	    ;;

	  ## Catch the login name if there is one.  Make sure the master
	  ## knows it.
	  ?,l*)
	    masteropts=("${masteropts[@]}" "-l$arg")
	    login=$arg
	    ;;

	  ## Catch the port number.  We want this for building the logfile
	  ## name.
	  ?,p*)
	    masteropts=("${masteropts[@]}" "-p$arg")
	    port=$arg
	    ;;

	  ## These options are interesting to the master connection.
	  m,[aADLlRSwxXv46]*)
	    masteropts=("${masteropts[@]}" "-${o:0:1}$arg")
	    ;;

	  ## SSH options on the command line merit special attention.  Pass
	  ## them onto the master, if necessary.
	  ?,o*)
	    masteropts=("${masteropts[@]}" "${opt:0:1}$arg")
	    case "$mode,$arg" in

	      ## User wants to control the process.  Let him.
	      ?,ControlMaster=* | ?,ControlPath=*)
		mode=p
		;;

	    esac
	    ;;
	esac
      done
      ;;

    ## A bare word.  Maybe it's the hostname, or the start of the command.
    *)
      case ${host-t}${host+nil} in
	t) host=$1 ;;
	*) break ;;
      esac
      ;;
  esac
  shift
done

###--------------------------------------------------------------------------
### Now to actually do the job.

## If there's no host, pass straight through.  We can't do anything useful
## anyway.
case ${host+t} in
  t) ;;
  *) mode=p ;;
esac

## Actually do something useful.
case "$mode" in
  p)
    exec "$REAL_SSH" "${opts[@]}" ${host+"$host"} "$@"
    ;;
  m)
    mkdir -p -m700 "$SSH_LOGDIR"
    logfile=$SSH_LOGDIR/${login+"$login@"}"$host"${port+":$port"}.log
    if ! "$REAL_SSH" -Ocheck \
      ${port+-p$port} ${login+"$login@"}"$host" \
      >/dev/null 2>&1
    then
      "$REAL_SSH" -MNf "${masteropts[@]}" "$host" \
	</dev/null >/dev/null 2>$logfile
    fi
    exec "$REAL_SSH" ${opts[@]} "$host" "$@"
    ;;
esac

###----- That's all, folks --------------------------------------------------